In operation of electronic circuits, power supply ripple rejection ratio (PSRR) is a measure of the capability of a circuit to reject ripple (also known as ripple voltage) that is coming from an input power supply. Ripple is a small periodic variation of the direct current (DC) output of the power supply, where ripple is generally due to incomplete rectification or suppression of an alternating current (AC) source that is rectified to generated the DC output. Ripple thus is an alternating component of a voltage from a rectifier or generator. PSRR may measure such capability at various frequencies.
An example of a linear regulator is an LDO (low dropout) regulator, which is a direct current (DC) linear voltage regulator producing a regulated power supply output. A LDO regulator is intended to maintain a specified output voltage over a wide range of load current and input voltage, where the difference between the input and output voltages is referred to as the dropout voltage. A linear regulator generally includes a power transistor and an error amplifier, which may also be referred to as a differential amplifier. For a linear regulator such as an LDO regulator, PSRR is a measure of the output ripple compared to the input ripple over a frequency range, which is generally a wide frequency range, such as, for example, 10 Hz (hertz) to 10 MHz (megahertz) expressed in decibels (dB).
However, linear regulators often do not provide sufficient rejection of ripple voltage. The remaining ripple voltage can affect circuit operation, or require additional efforts to control the remaining ripple in the power supply output from the linear regulator.